Shielding for radio apparatus



A. C. PECK SHIELDING FOR RADIO APPARATUS Dec 25, 1928 Filed Sept. 9,1927 Admlh. EL. fi

Patented Dec. 25,, 1928.

UNITED STATES Anonrn cnor'ron wax, or SANDUSKY, onro.

SHIELDING FOB RADIO APPARATUS.

Application filed September 9, 1927.- Serial No. 218,519.

The present invention relates to an improved shield constructionprimariLy intended for use in connection with radio receiving apparatus.

In ra-d1o receiving apparatus employing multiple stages of amplificationat radio frequency, it is essential that the individual stages be soisolated as to prevent electromagnetic couplin between the units orstages, other than t rough their proper channels. With the usual methodnow employed for shieldin a solid metal sheet is used, and this form 0shielding acts as a distributing agent with the result in interferencebein nearly as great as if no shielding were use This solid metal sheetconductor when used as a shield in radio receiving circuits, adds agreat amount of resistance to the receiver. as a whole, where the tuninginductances and condensers come in close contact to the shielding, andresulting in the capacityofv the receiver being reduced to a point wherein some cases, an extra stage or unit of amplification is required tocompensate for the losses so incurred. Currents generated at radiofreuency will penetrate any substance wit the exception of metal, and ascertain metals have higher conductivity than others, the quantity ofmetal employed in the usual sheet metal shields, together with itsproperties as a conductor for high frequency current, will naturallydetermine the amount of resistance added to the receiver when using 'ametal shield. Whenusing a solid sheet metal conductor for shieldingpurposes, it is necessary to use a fairly thick sheet in order to'oifsetthe tendency of the sheet to warp or buckle due to atmospher c changes,and which buckling or distortion of the sheet causes capacity changes inthe a paratus or possible short circuit due to the shielding contactingwith the circuit, andboth of which woul tend to impair that over allefliciency of the receiving apparatus It is therefore a primary objectof the resent invention to provide'an improved s reld for radioapparatus embodying the operating characteristics of the solidmetalshield withoutthe inherent losses 'due to the.employ ment' of" suchsolid sheet metal conductors.

A further object of theinvention is to provide a novel and improvedshield for radio a paratus which may, be employed for either-e lminatinginterference due to exterin which drawing:

nal sources or as means to prevent interstage coupling between radiofrequency units other than through their proper connecting channels.

A further object of the invention is to provide a flexible shield forradio apparatus whlch may be employed as a lining for the panels andcabinets that house the apparatus, in a manner whereby the signal to bereceived mayl only pass to the receiving circult throng the properantenna binding post.

Other objects and advantages of the invention will be apparent duringthe course of the following detailed description, taken in connectionwith the accompan ing draw mg forming a part of this speei cation andFigural is an enlarged fragmentary plan v1ew of the improved shieldshowing cer tain sections thereof removed and others broken away forillustrating the specific detail of construction.

Figure 2 is an enlarged fragmentary section through a section of theshield.

Figure 3 is an enlarged longitudinal section through one of theconductor leads forming'a part of the'shield.

Referring to thedrawin in detail, and whereinsimilar reference 0 ractersdesignate cor-responding parts t roughout the several views, the letterA may desi ate as a whole, the improved shield which embodies asupporting base B, a series of conductor leads C supported by thebase'B, a contact base or coating D afiixed to the base B as by a binderE, and F mounting means for securing the shield in adjusted relation forshielding purposes.

The base B is of a flexible nature and 'preferably consists of a 'sheetof woven fabric'such as muslin of the like wove in the usual' manner toform warp and woof threads5 and6 respectively, and the weave of thefabric is*preferably like that illustrated. in Figure 1 of the drawing.The fabric may of course'be of either close or coarse'weave for eithercausing the adjacent threads; 5 or 6 to be either contacting one withthe other or spaced a suitable dis .tance so that relatively smallopenings are provided between the crossed" threads.

While the sheet like supporting base B has been shown as being 0 fabric,the same A g A I .the same preferably consist of strands of tinselledwire embodying a carrier thread 7 about which is spirally Wound asubstantially fiat copper'strip 8 which may either be wound with ends ofadjacent convolutions in contacting engagement or slightly spaced asclearly illustrated in Figure 3. These conductor leads C are preferablywoven directly into the fabric supporting base B during weavii'ig of thefabric so that adjacent runs of the leads are suitably spaced by thewarp and weft threads 5 and 6 respectively so that the leads form asubstantially net like construction with the leads contacting one withanother at their traversing points. Thus it will be seen that theeonductor leads form an open work construction intended to be supportedby the fabric -B with the traversing leads in electrical contact onewith another. Owing to the high electrical conductivity of copper, it ispreferred that the conductor leads be so formed for reducing theabsorption effect of the shield.

As in usual practice, the shield A when associated with the radioreceiving set will be at a ground potential by connecting the net likeconstruction of the conductor leads directly to a ground connectionthrough a suitable binding post provided on the receiving a partus.

Re erring now to the contact face or coating D, the same is formed ofmetal frag ments preferably aluminum filings. These metal fragments areintended to be afiixed in a mass to one side of the fabric base B as bymeans of the binder E, the binder serving both as means for retainingthe metal fragments in a compact arrangement and also as means forsecuring the coating to the supporting base. The metal fragments formingthe coating D are so applied to the supporting base that the fragmentsare in electrical contact with one another and with certain of the inelectrical contact with the conductor leads C as is clearly illustratedin Figure 2. Thus it will be seen that the metal fragments of thecoating D may be effectively grounded through the conductor leads G.Since aluminum is of low electrical conductivity in comparison to othermetals such as brass and copper, it will be seen that when the shieldingis placed in relatively .close contact with apparatus of the receivingcircuits, that loss through induction to ground will be at a minimum. I

The binder E may in the form of a gum varnish, or of a material bearingadhe sive characteristics and. bein of a nature to exclude moisture fromthe fa ric base B and metal fragments yet allow for the shield structureto be of a flexible nature owing to the elasticity of the binder.

It may here be well to state that the shielding A as a finished product,will resemble somewhat emery cloth inflexibility, and the metalfragments forming the contact face or coating may be applied to thesupporting base much in the same manner as are the emery fragmentsapplied to the cloth in manufacture of emery cloth.

It will be observed that the coating D of metal fragments, forms a sheetlike covering for one face of the supporting base and forms asubstantially flat surfaced coating having low conductivity and being inelec- 'trical contact with the conductor leads 0 which are intended tobe connected with a suitable ground terminal.

As to the mounting means F, the same in the example shown is in the formof an adhesive such as gum arabic applied to the opposite surface of thesupporting base B from that at which the coating D is formed. Thus itwill be seen that when applying the shield for shielding purposes, theadhesive may be dampened or softened and then the shield appliedpermanently to the panels and sides of the cabinet of the radioapparatus. WVhen so applying the shield, the same will form a metalbarrier which entirely surrounds the receiving circuits, and byconnecting the leads G with a suitable ground connection, the shieldwill be maintained at a ground potential. WVhen so enclosing thereceiving circuit apparatus, it will be seen that the apparatus will beeffectively shielded against interfering electrostatic charges andelectromagnetic waves, and that the only'path through which a signal maybe received and passed through the various tuning circuits, will be fromthe antenna directly to the antenna binding post of the receiver. 7

The shield may of course be used in a receiving apparatus to isolate theindividual units or circuits with a minimum resistance and distr-ibutincapacity.

\Vhen so app ying the shielding as b the adhesive F to the interiorsurface of a ousing for radio receiving apparatus, it will be seen thatthe shield becomes permanently fixed and will not be affected by varyingclimatic conditions. A shielding such asdisclosed may be very easily andquickly applied, since the same is capable of being readily cut by aknife or pair of shears to the exact size of the surfaces being coveredby the shieldin which the shielding is made may of coursebe of anyrequisite dimension in accordance with the requirements of the trade.

From the foregoing description it will be apparent that a novel andimproved shield for use in connection with radio receiving A size of thepiece ofto' absorption and interference due to dis- .groundin tributingeffects, will be reduced to a miniwith said conductor leads throughoutthe apparatus has been provided which is of a flexible sheet likesupporting base, a flexible flexible sheetlike nature such as to allowgrounding conductor carried by the base, for ready and easy installationof the shieldand a facing of fra ing, andwhich shield embodies novelhav-in electrical con uctivity, afiixed to features of constructionwhereby losses due said ase in electrical contact with the flexed witthe supporting base. mum. 8. In a shield of the class described,-aVarious chan es in the shape, size and. flexible sheet like supportingbase,a flexible s ecific materia defined may be ,made to net like screenhaving electrical conductivdescribed, without departing from th of theinvention or the scope of the in claims.

e spirit ing aflixed to one face of the supporting fol owbase embodyingmetal fragments having I electrical contact'with said screening. claim:9. In a shield of the class described, a 1. In a shield of the classdescribed, a flexible sheet like supporting base, a flexible entitiousmaterial conductor and capable of being t e form of the invention hereinshown and ity, carried by said base, and a flexible coatsheet likesupporting base, a facing of fragnet like screening havinghighelectrical mcntitious material having electrical conconductivity,carried-by said base, and a ductivity aflixed to said base, anda'groundflexible coating aflixed to one side of said ing conductorca-rried' by the base and havbase embodying metal fragments of low ingelectrical contact. with the facing-at electrical conductivity, saidfragments conspaced points throughout the area thereof. tactingone withanother and being in elec- 2. In a shield of the class, described, atrical contact with said screenin sheet like sup orting base, a not likescreen- 10. In a shield ofthe class escribed, a ing having e ectricalconductivity, carried flexible, sheet like su porting base, a flexbysaid base, and a facing of fragmentitious ible net like screen havingelectrical conmaterial having electrical conductivity, afductivity,carried by said base, a flexible fixed to said base and in electricalcontact coating afiixed to one face of the sheet like.

with the strandsof screening. supporting base embodying metal frag- 3.In a shield of the class descrlbed, a ments having electricalconductivity and sheet like supporting base, a net like screenhavingelectrical contact with said screens mg havm high electricalconductlvlty, caring, and an adhesive carried by the-opposite ried bysa1d,base,a-nd a facing 0f fr gmen face of the sheet like supportingbase from tious material having low electrical. conducid coating.tivity, aflixed to said base and in electrical 11. In a shield of theclass described, a contact with the strands of said screening. fabricsheet forming a supporti o b 4- In a ield o the Class E Q- it a ductorleads interwoven into the a ric sheet sheet l1ke su porting base,traversing conin spaced apart relation, anda flexlble coatductor leadsaving electrical conductivity, ing aflix d to the supporting baseembodysupported in spaced apart relation on the ing metal fra ents avingelectrical conbase, and a facing of fragmentltious matem t with s iconductor leads at spaced said base and being" in electrical contact i barea of the facing. i fabric sheet forming a supporting base, conrialhaving electrical conductivity, aflixed to points throughout the areaofthe support- 12. In a shield of the class described, a I

5. In a shield of the class describ a ductor leads interwoven 1n thefabric in Sheeblike pp g b a net like S IP- traversing relation andcontacting one with ing of interwoven conductor leads having noth t th itraversing i t and a electrical conductivity, supported by the' facingof fragmentitious material having in electrical contact with theconductor lead of said screenin base, and afa ing f gm ll mateelectricalconductivity, affixed to one face rial having electrical conductivity,aflixed to of the fabric sheet in electrical contact with one face ofthe sheet like supporting base aid ccnductcrleads.

I fabric sheet embodying warp and weft .6. In a $1116]. of the classdescribed, a threads, conductor leads "interwoven in sheet likesupporting base, conductor leads spaced relation in .thefabrie inparallel rehaving electrlc'al conductivity, interwoven lation with boththe warp and weft threads,

13. In a shield of the class described, a]

in traversing relation into the supporting a flexible coating aflix'edto one face of the base with adjacent parallel leads spaced fabricembodying metal fragments having from one another, and. a facing offragelectrical contact with said conductor leads,

. ing base in electrical contact with said contion of the shield forshielding purposes.

I ductor leads.

' I 14'. In a shield of the class described, a 7. In a shield of theclass described, a fabric sheet forming a supporting base, conmentitiousmaterial having electrical 'conand an adhesiveaflixed to the oppositeface 'ductivity aflixed toone face of the supportof the fabric'from saidcoating for applicaductor leads interwoven in the fabric emductor leadsinterwoven in the fabric sheet 10 bodying carrier threads havingspirally embodying carrier threads and copper strips Wound thereonstrips having electrical conspirally Wound about the carrier threads.ductivity, and a coating afiixed to one face and a coating atlixed toone face of the tab- 5 of the fabric embodying metal fragments ricembodying aluminum fragments being:

having electrical contact with the strips of in contact one with anotherand in electrical 15 said conductor leads. contact with the strips ofsaid conductor 15. In a shield of the class described, a leads. I fabricsheet forming a supporting base, con- ADOLPH CROFTON PECK.

